The invention relates to a method of and to an apparatus for producing electrical wires. More particularly, this invention concerns an arrangement which produces electrical conductor wires, especially profiled heavy wires, by insulating the wires with varnish hardenable through ultraviolet radiation.
It is generally known to apply continuously insulated varnish onto a red hot and possibly pretreated wire and to calibrate the thickness of the varnished layer by stripping off superfluous varnish before hardening the varnished layer through outer influence of heat. The solvent contained in the insulating varnish is vaporized upon simultaneous cross linkage of the varnished film on the conductor since a thermochemical reaction is obtained which is caused by the heat energy. The varnished film so hardened forms a well adhering as well as heat resistant and mechanical proof insulation on the surface of the conductor. Through selection of the insulating varnish, it is possible to adapt the properties of the insulation to special purposes of use as it is described in the West German published application AS No. 10 33 291.
This known finishing technique seems to be rather sound concerning the quality of varnish wires so formed; however, it has the disadvantage, that the unhealthy vapor of solvent is released during the hardening and is subjecting therefore a relevant environment to contamination. Since the solvent which amounts up to 70% of the quantity of the applied insulating varnish cannot be recovered, high manufacturing and production costs are caused which are even increased by the high expenditure of energy and the high yield of waste which is unavoidable upon each starting of a manufacturing device and means for drying and hardening.
A still further problem of this known method are the high manufacturing expenses due to the means for drying and hardening, the use of which is very difficult when manufacturing varnished wires of different cross section and is impossible for greater diameters as for example for profiled heavy wires. Therefore, these profiled heavy wires are insulated by winding.
From the West German published application AS No. 24 59 320, there is known a method of and an apparatus for producing a protective layer of synthetic onto light wiring fibers, especially glass fibers. The fibers are coated by a liquid polyester resin hardening by ultraviolet radiation wherein the thickness of the layer is kept constantly by a stripper. The fiber so coated is then guided through a tubular ultraviolet radiator whose intensity of radiation is synchronized to the desired manufacturing rate so that the coating is bubble-free, smooth and cured after leaving the radiator. The thickness of the coating can be controlled under consideration of the viscosity of the liquid resin and the elasticity of the cured protective layer is adjusted by mixing different resins hardened through ultraviolet radiation.
The apparatus disclosed in this reference has a storage container for the polyester resin which is connected to a coating container via a level regulating device. In the bottom of the coating container, there is an entrance opening for the light wiring fiber which opening is sealed by a capillary tube. A stripper, one or several shields against ultraviolet radiation and a tubular ultraviolet radiator are arranged directly above the surface of the coating container.
The liquid coating used in this method contains photoinitiator systems in opposition to the common insulating varnish for conductor wires, thereby hardened and cross linked solely through the radiation with ultraviolet light which radiation is relatively poor in energy. There is no need to separate solvents by vaporizing which could contaminate the environment and causes the high expenditure on heat energy in common hardening of insulating varnish. Therefore, efforts were made to use such coating for the production of insulated electrical conductor wires.
It has been recognized, however, that the known method was not satisfactory when using in that field since it has been found that the different properties necessary for the insulation of the varnished wire were not sufficient when determining the properties of the cured coating by mixing different liquid coating materials hardenable through ultraviolet radiation. The insulation of electrical conductor wires must have different properties, like a good adhesion on the metallic conductor surface, a flexibility, high electrical insulating quality, heat resistance and mechanical strength, especially resistance against abrasive and a mar-resistance which properties cannot be achieved simultaneously by a known coating material or by a mixture thereof.